1. Field of the Invention
The present invention relates to a particle detector system. Also, the present invention relates to a lithographic apparatus comprising such particle detector system. The particle detector system may be used for detection of unwanted particles on a substrate before or during patterning of the substrate in a lithographic apparatus. Further, the present invention relates to a particle detecting method, and a device manufacturing method.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus may be used, for example, in the manufacture of flat panel displays (FPDs), integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which may be referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern may be transferred on (part of) the substrate (e.g., a glass plate), for instance via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning device may be used to generate other patterns, for example a color filter pattern, or a matrix of dots. Instead of a mask, the patterning device may comprise a patterning array that comprises an array of individually controllable elements. A benefit of such a system compared to a mask-based system is that the pattern can be changed more quickly and for less cost.
A flat panel display substrate may be rectangular in shape. Lithographic apparatus designed to expose a substrate of this type may provide an exposure region which covers a full width of the rectangular substrate, or which covers a portion of the width (for example half of the width). The substrate may be scanned underneath the exposure region, while the mask or reticle is synchronously scanned by the projection beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure may be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate may be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
Current systems for Flat Panel Displays (FPD) lithography use a mask that is imaged onto a substrate, as described above. In maskless FPD lithography systems, a part of the lithographic apparatus—usually an imaging system or an optical component thereof, such as a lens—is arranged relatively close to the substrate which is moving during imaging. The distance between the imaging system and the substrate may be in the order of several mm or less, down to for instance 0.1 mm. If particles or other contamination (which will be deemed to be included in the term “particle” used herein) are present at the substrate surface, they may damage the imaging system during passage thereof when they have a height (a dimension perpendicular to the substrate surface) which exceeds the distance between the imaging system and the substrate. Such damage will incur relatively high costs, for instance for replacing at least part of the imaging system but above all due to a decrease in production caused by the downtime of the lithographic apparatus. The particles may include, but are not limited to, glass particles, resulting from machining and handling a glass substrate. The relatively high travel speed of the substrates used for FPD production, in the order of meters per second (m/s), as well as the relatively large dimensions of the substrates, in the order of meters, both in width and in length, may further complicate the manufacturing process.